1. Field of the Invention
The present invention relates to temperature sensing and, more particularly, to temperature sensing using contact sensors.
2. Description of the Related Art
Temperature sensing using temperature sensors has in the past been performed in many ways for many purposes. In general, temperature measurement can be divided into two categories: contact temperature measurement and non-contact temperature measurement. In the contact category, temperature sensing devices contact a surface whose temperature is to be measured. In effect, the contact temperature sensors measure their own the temperature and tend to be slow in responding to temperature changes. On the other hand, in the non-contact category, temperature sensors measure optical emission (e.g., infrared radiation) emitted from the surface. The non-contact temperature sensors tend to respond more quickly than contact temperature sensors, but are more expensive.
In situations in which the temperature sensing must occur during the presence of significant amounts of radio frequency (RF) interference, the temperature sensing is made more difficult. Specifically, the RF interference tends to interfere with electrical signals that represent the temperature measurement. Hence, temperature measurement is often not possible because the electrical signals normally used to represent the temperature measurement are overwhelmed by the RF interference. One example of an environment having significant amounts of RF interference is semiconductor manufacturing equipment such as semiconductor wafer processing equipment where RF signals are used to generate discharges.
For contact temperature measurement, there are various ways to measure temperature, e.g., thermistors, resistance temperature devices (RTD), thermocouples, platinium resistance bulbs, bulk silicon devices and solid state devices, but temperature sensing in an environment having significant RF interference remains technologically challenging as temperature sensors pickup the RF interference. Another problem with contact temperature measurement is that the temperature sensors can perturb the RF tuning of the discharge in a semiconductor processing chamber. With the RF tuning perturbed, the processing within the semiconductor processing chamber is no longer reliable.
For non-contact temperature measurement, infrared and phosphor fluorescence techniques can be used for temperature sensing in a RF environment. Some of these optical approaches are able to utilize optical isolation to avoid the RF interference, others are not. The optical isolation could, for example, be provided by shining pulsed ultraviolet light onto a phosphor which is coated on a surface, then determining the temperature from the reflected photons from the phosphorous surface. The optical isolation could alternatively use the amount of infrared light emitted from a surface to determine the temperature. Some infrared techniques, such as infrared thermocouples, remain affected by RF interference. Even if these optical approaches are able to provide optical isolation that mitigates RF interference, there are some problems with these approaches.
Within a processing chamber, there is a glow discharge that produces a full spectrum of electromagnetic radiation ranging from RF, microwave and infrared to visible and ultraviolet lights. One problem is that the optical approaches must deal with the optical interference from the glow discharge internal to the processing chamber. The ability to monitor temperatures internal to a processing chamber is desirable because temperature plays a significant role in the semiconductor processing performed in the processing chamber and variations in temperature can cause processes to vary and therefore fail. More particularly, in the case of semiconductor manufacturing equipment, the temperature of various components within the processing chamber affects the processing performed by the semiconductor manufacturing equipment. For example, in the case of etching, the etch process should occur within a predetermined temperature range and when the temperature exceeds the predetermined temperature range, the etching reactions will be altered, thereby causing the etch process drift. More seriously, if a processing chamber is overheated for an extended length of time, but not noticed by the operators because of lack of temperature monitoring, the process chamber can be seriously damaged. In this case, the semiconductor processing equipment must be shutdown for maintenance, Any major shutdown of equipment in a semiconductor manufacturing environment will increase the cost of production and should be prevented if possible. Another problem with these optical approaches is that the cost for such temperature monitoring systems is expensive, since a spectrometer or other sophisticated electro-optic instruments may be used.
Hence, there is a need for improved techniques to monitor temperatures internal to processing chambers of semiconductor manufacturing equipment.